Antenna selection method

ABSTRACT

A method and apparatus for initiating a telecommunications uplink from a mobile terminal to a telecommunications network. A preamble signal is transmitted from the mobile terminal to the network in accordance with a transmission parameter of the mobile terminal. The parameter is changed and the preamble retransmitted until successful receipt in the network is confirmed. Changing the transmission parameter alters the signal diversity of one or more preambles as received by the base station.

FIELD OF INVENTION

The present invention relates to the field of parameter selection inrelation to antenna, beam and carrier selection in mobiletelecommunications devices, and more particularly to selection methodsand apparatus for reducing connection establishment time in suchdevices.

The invention has been developed primarily for use in 3rd generation(3G) wideband code division multiple access (WCDMA) systems, and will bedescribed hereinafter with reference to this embodiment. However, itwill be appreciated that the invention is not limited to use in thisarea.

BACKGROUND TO INVENTION

MIMO (Multiple-Input Multiple-Output) and transmit diversity techniqueshave provided attractive solutions for increasing downlink capacity inwireless mobile networks and currently MIMO is being considered forWCDMA (Wideband Code Division Multiple Access) standardization fordownlink transmission.

For various reasons, uplink multi-antenna transmission solutions havenot been given much attention to date. In order to keep the costs andcomplexity of such handsets acceptable, it has been proposed that theyonly include a single full transmit (ie, uplink) chain and two receiver(ie, downlink) chains.

Lack of signal diversity can be a problem when transmitting commonchannels in a mobile telecommunications system. In the case of a mobilehandset attempting to use the random access channel (RACH) procedure toestablish an uplink (or two-way) connection, soft handover is notpossible and thus no macro diversity gain can be obtained. The diversityproblem exists if there is no (or only a small amount of) multipath ortime diversity available in the radio channel.

Typical steps involved in the RACH procedure are shown in FIG. 1. Aninitial preamble P0 is sent by user equipment UE at a first, relativelylow power. The downlink power is measured and the transmit power of theinitial preamble P0 is set (based on the DL measurement) with the propermargin due to the open loop inaccuracy (open loop power control notbeing particularly accurate, since it is difficult to measure largepower dynamics accurately in terminal equipment). Transmission of thefirst and subsequent preambles is commenced at the beginning of any of anumber of pre-defined time slots, known as access slots. There are 15access slots per two frames, and they are spaced 5120 chips apart. Aftertransmitting the first preamble P0, the UE decodes the acquisitionIndication Channel (AICH) to determine whether the base station BS hassuccessfully received the preamble. In the event the first preamble P0is not acquired by the BS, the power level is raised (typically by 1 dB)and a second preamble P1 sent at the new power level in the nextavailable access slot. The AICH is decoded to check whether the BSreceived P1, and the process is repeated for further preamble signals,until a power level is reached where the AICH indicates reception of thelast transmitted preamble at the BS.

Once a preamble is acknowledged by the BS, the UE transmits the 10 ms or20 ms long message part that consists of control and data parts of theRACH transmission (transmission power of the message part is typicallybased on that of the latest (successful) preamble). For example, an IPaddress can be carried using the data part.

Whilst the UE is performing the RACH procedure, it is possible that theradio link between the UE and the BS is in deep fade. This means thatmultiple sequential preambles (with increased transmit power) must betransmitted to compensate the channel attenuation and to get theacceptable performance for the RACH reception. This increases the timetaken for the RACH process to be successful, and in the meantimegenerates more interference to the other users of the RAN (Radio AccessNetwork). Power consumption is also increased at the UE, which has adeleterious effect on battery life.

SUMMARY OF INVENTION

In accordance with a first aspect of the invention, there is provided amethod of initiating a telecommunications uplink from a mobile terminalto a telecommunications network, the mobile terminal having atransmission chain including a baseband stage, a power amplificationstage and an antenna, the method including the steps of:

(a) transmitting a preamble signal from the mobile terminal, thepreamble signal being transmitted in accordance with a transmissionparameter of the mobile terminal;

(b) determining whether a base station has successfully received thepreamble signal and if so, establishing an uplink to the base station onthe basis of the first transmission parameter;

(c) in the event it is not determined that a base station hassuccessfully received the preamble signal, changing the transmissionparameter, and repeating steps (a) and (b);

-   -   wherein the transmission parameter controls one or more of the        baseband stage, power amplification stages and the antenna such        that changing the transmission parameter in step (c) results in        an alteration of the signal diversity of one or more preambles        as received by the base station.

Preferably, the transmission chain includes at least two antennae, andthe transmission parameter determines which of the antennae the preambleis transmitted from. More preferably, the preamble is transmitted fromonly one of the antennae at a time.

In one embodiment, the transmission parameter includes a frequency band,each preamble being transmitted via the frequency band indicated by thecurrent transmission parameter.

In another embodiment, the transmission chain includes a plurality ofantennae in an antenna array. Directionality of a beam formed by signalstransmitted from the array is selected for each preamble transmissionbased on the transmission parameter. Preferably, the transmission chainincludes a phase shifting means for shifting the phase of the signalssupplied to the individual antennae in the antenna array, the phaseshifters being controllable on the basis of the transmission parameter.

In a preferred embodiment, the uplink is established in accordance withthe transmission parameter used when the base station successfullyreceived the preamble.

Preferably, the transmission parameter includes a power level at whicheach preamble is transmitted, the power level being increased between atleast some sequentially adjacent preamble transmissions.

According to a second aspect of the invention, there is provided amobile telecommunications terminal configured to initiate atelecommunications uplink to a telecommunications network, the mobileterminal having a transmission chain including a baseband stage, a poweramplification stage and an antenna and being configured to:

(a) transmit a preamble signal in accordance with a transmissionparameter of the mobile terminal;

(b) determine whether a base station has successfully received thepreamble signal and if so, to establish an uplink to the base station onthe basis of the first transmission parameter;

(c) in the event it is not determined that a base station hassuccessfully received the preamble signal, change the transmissionparameter, and repeat (a) and (b);

-   -   wherein the transmission parameter controls one or more of the        baseband stage, power amplification stages and the antenna such        that changing of the transmission parameter in (c) results in an        alteration of the signal diversity of one or more subsequent        preambles as received by the base station.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the present invention will now be described, byway of example only, with reference to the accompanying drawings, inwhich:

FIG. 1 is a graph showing the structure of a prior art common packetchannel (CPCH) access transmission;

FIG. 2 is a graph showing the structure of a CPCH access transmission,according to the invention;

FIG. 3 is a graph showing the structure of an alternative CPCH accesstransmission embodiment, according to the invention;

FIG. 4 is a schematic of a transmission chain in a mobile terminal, inaccordance with the invention;

FIG. 5 is a schematic of an alternative transmission chain in a mobileterminal, in accordance with the invention;

FIG. 6 is a schematic of yet another transmission chain in a mobileterminal, in accordance with the invention; and

FIG. 7 is a schematic of an alternative transmission chain in a mobileterminal, utilising a Uniform Linear Antenna (ULA) array.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the drawings, there are shown a number of embodiments ofthe present invention, in which establishment of an uplink from a mobilehandset is improved by changing transmission parameters between preambletransmissions. The intent of changing the transmission parameter is toimprove the signal diversity between preamble transmissions, so as toincrease the chance of each subsequent preamble transmission beingsuccessful.

Referring to FIG. 1, there is shown a series of steps taken over a timeperiod to establish an uplink. The embodiment illustrated is a CommonPacket Channel (CPCH) access transmission. More detail of the steps usedin establishing an uplink channel via this procedure are detailed in“Physical Channels and Mapping of Transport Channels Onto PhysicalChannels (FDD)”, v. 4.2.0, 3GPP, TS 25.211, the contents of which areincorporated herein by way of cross-reference. It will be appreciatedthat the steps involved are similar to those in the procedure applied toestablishing a Random Access Channel (RACH), and correspondingprinciples apply in such an embodiment.

As described in relation to the prior art, the UE can start therandom-access transmission at the beginning of any of a number ofwell-defined time intervals, denoted access slots. There are 15 accessslots per two frames and they are spaced 5120 chips apart. The timing ofthe access slots and the acquisition indication is known to thoseskilled in the art and so is not described here in any detail.

Initially, a first preamble P0 is transmitted from a User Equipment (UE)at a first, relatively low, power level (based on DL measurement), whichtakes around 1 millisecond. This is performed in accordance with a firstvalue of a transmission parameter. The meaning of “transmissionparameter” is described in more detail in relation to the followingembodiments.

After a short delay, the UE decodes the AICH (Acquisition IndicationChannel) to see whether a Base Station (BS) has detected the preamble.In the event the UE detects that a BS has detected the preamble, it ispresumed that the present power level is acceptable. However, in thepresent case, no BS has responded, so the UE increases the power level,changes the transmission parameter and retransmits the preamble. It isthe changing of the transmission parameter that distinguishes thepresent invention from the prior art.

The steps of changing the transmission parameter and (in the preferredembodiment) the transmission power are repeated until the power cannotbe increased any more, the operation times out or the AICH indicatesthat a BS has received the preamble.

Once the AICH has successfully been received by the UE, a collisiondetection (CD) procedure is performed. Collision in the CPCH means thattwo UEs have selected the same access channel and preamble at the sametime. Using the CD mechanism, the probability of collision is decreased.WCDMA system utilises the CD mechanism in the Physical CPCH but it isnot used in the Physical RACH. In the CD procedure, the UE randomlyselects a CD signature and a CD access slot subchannel, then transmitsthe CD preamble. If the UE does not receive the CD-AICH in thedesignated slot it aborts access. If the UE receives the CD-AICH in thecorrect timeslot with matching signature, it continues the connectionestablishment (i.e., transmits possibly the power control preamble andfinally starts data transmission immediately afterwards).

The transmission parameter can take many forms, some of which aredescribed in relation to the embodiments in FIGS. 4 to 6. It will beappreciated that the UE in each case includes considerably more featuresand circuitry than that shown. However, for the purposes of clarity,only the minimum features necessary for understanding the invention areshown. For example, in addition to the various transmission chaincomponents shown, most UE will also have a reception chain for, at thevery least, receiving and decoding an acknowledgement signal from a BS.

Referring to FIG. 3, there is shown a UE 300 in the form of mobiletelephone. It will be appreciated that the UE can take the form of anymobile telecommunications device, such a Personal Digital Assistant(PDA), portable computer, or any combination of devices capable ofcommunicating via a radio telecommunications network.

The UE includes three main functional aspects: a baseband stage 302, apower amplification stage 304, and, in this case, two antennae 306 and308 connected to the output of the power amplification stage 304 via aswitch 310. The baseband stage 302 does all of the manipulation requiredto take a digital voice or data signal and perform RF processing suchthat the voice or data can be transmitted from the UE. The basebandstage 302 also manipulates control signals and any other data that needsto be transmitted from the UE.

The power amplification stage 304 takes the processed signal from thebaseband stage 302 and amplifies it, before supplying it to the switch310. The switch 310 is controlled by UE controller 312 to supply theoutput of the power amplification stage 304 to either the first antenna306 or the second antenna 308, as required. It will be appreciated thatin the usual case where the antenna is for transmitting and receiving,the switch can also be controlled to switch either or both of theantennae to a receiver chain, depending upon the configuration andrequirements of the UE and the network within which it operates.

To initiate an uplink connection, the baseband stage 302 provides afirst preamble signal to the power amplification stage 304. The UEcontroller 312 controls the power amplification stage such that itoutputs a first, relatively low power signal, whilst the switch 310 iscontrolled to feed the output of the power amplification stage to thefirst antenna 306,from which the preamble is transmitted.

Once the first preamble has been transmitted, the UE decodes the AICHvia the receiving chain (not shown) to ascertain whether a BS hasreceived the preamble. If the AICH is not detected, then thetransmission parameter is changed. In the embodiment of FIG. 3, thismeans that the switch is controlled to reroute the output of the poweramplification stage 304 to the second antenna 308.

In one embodiment, the preamble is then re-broadcast at the appropriatetime to coincide with the next access slot, at a higher power level thanthe first transmission at time t_(j). If the AICH is not then detected,the power is increased and the preamble retransmitted. Theretransmission at this stage can be to either the first or the secondantenna, although it will usually be preferable to switch back to thefirst antenna for the third transmission of the preamble. If the AICHcontinues not to be detected, then the preamble is retransmitted withthe power level increasing with each transmission, and the antenna beingswitched either every transmission or every second transmission.

FIG. 2 shows an embodiment of such a scheme, in which the powerincreases with each preamble transmission. The antenna, in this case, isswitched only every second transmission after the first twotransmissions. In this case, the preamble is successfully received bythe first antenna at time t_(j) at power p_(j).

In an alternative embodiment, shown in FIG. 3, the power is notincreased with each preamble transmission after the first; rather, it isonly increased every second transmission. It is indicated under eachpreamble transmission in FIG. 3 which antenna is used, A₁ being thefirst antenna and A₂ being the second. The antenna sequence shown is(A₁, A₂, A₂, A₁, . . . ), but this could also be (A₁, A₂, A₁, A₂, . . .) due to the additional diversity offered by the antenna swapping. Inthe illustrated case, the preamble is again received at time t_(j) atpower p_(j), but it will be noted that antenna A₂ is selected, and thatpower p_(j) is the same as for the previous preamble sent at time t_(j).

In the embodiments of FIGS. 2 and 3, the effect is that eachtransmission will have a different chance of reaching a BS, because itwill be via a different antenna and/or at a different power to theprevious preamble transmission.

The structure of FIG. 4 can also support other embodiments. For example,in addition to altering the antenna through which the preamble is beingtransmitted, the transmission parameter can also switch the basebandfrequency to that of a different carrier. In proposed WCDMA systems,carrier spacing is 5 MHz, meaning that there will be relatively littlecorrelation between even adjacent carriers when considering fast-fadechannel characteristics.

Turning to FIG. 5, there is shown an alternative embodiment of the UE300 shown in FIG. 4, wherein like features are indicated with likenumerals. However, in this case, there are two parallel poweramplification stages 400 and 401, which accept the output of thebaseband stage 302 via a switch 402. The operation of the UE is similarto that described in relation to the FIG. 4 embodiment, except that theswitch 402 is responsive to a transmission parameter to determine whichantenna the preamble is being sent to. The power amplification stagesare individually controlled such that the output power is ramped upevery (or every second) preamble transmission.

Another embodiment of the invention is shown in FIG. 6, in which thereare two complete parallel transmission chains. In this case, there is noneed for a switch to control which antenna receives a signal. Rather,the UE controller determines which baseband stage outputs the preambleat any given time. In this case, it is even possible to transmitpreambles simultaneously, thereby further reducing the average accesstime, albeit with a power consumption penalty. This embodiment alsoallows increased data rates, because the transmission chains can beoperated to transmit data simultaneously once the preamble procedure iscompleted.

In each of the precious embodiments, there is disclosed a pair ofantennae. However, it will be appreciated by those skilled in the artthat further diversity can be attained by incorporating additionalantennae in the UE and correspondingly modifying, or adding to, thedisclosed transmission chains.

The embodiments can also be modified to take into account steered beamtransmission via a ULA (Uniform Linear Antenna) array of any suitablesize and configuration. FIG. 7 shows an example in which a ULA 70includes first and second antennae 71 and 72, which are spaced apart by(lambda/2), where lambda is the wavelength of the signal of interest.The first and second antennae 71 and 72 are fed signals from a poweramplifier 304 by way of respective phase shifters 73 and 74. The phasechange of each phase controller is independently controlled by the UEcontroller 312. Using this arrangement, it is possible to generate two(or more) fixed beams in pre-defined directions (e.g., ±90 degrees). Thebeams are controlled by the UE controller via the phase shifters suchthat the signal is transmitted directionally, as is well understood bythose skilled in the art of beam-steering. In this embodiment, thetransmission factor is the direction of the beam. By changing the beam(and optionally the carrier frequency), antennae diversity is improvedover multiple attempts at transmitting a preamble.

It will be appreciated that the embodiment of FIG. 7 can be altered suchthat the power amplifier 304 is removed and replaced with individualamplifiers between the phase-shifters 73 and 74 and their respectiveantenna 71 and 72.

It will be understood that in all the ULA embodiments, other numbers ofantennae can be used.

Thos skilled in the art will appreciate that certain combinations of thedifferent embodiments can be used, as long as the overall diversitychanges between at least some preamble transmissions.

The present invention provides a number of embodiments of a system inwhich antennae diversity is used in establishing an uplink connectionfrom a mobile telecommunications device in a radio telecommunicationsnetwork. The preferred embodiment is applied in a 3GPP WCDMA FDD system.However, it will be appreciated that the invention has application underother standards where improved antennae diversity provides animprovement over simply ramping up power over multiple preambletransmission attempts. For example, GSM/EDGE uses a similar RACHprocedure to that described above, although the corresponding timedelays are longer and thus reductions in time delay arising fromimproved antennae diversity are likely to be smaller than the WCDMAcase.

The main advantage arising from the preferred embodiments is a (onaverage) shorter RACH procedure. This will speed up the call setupprocess and cause smaller delays for user data transmission on RACH andCPCH. This means that the transmission time that is needed to transmitsmall data packets via uplink RACH and CPCH is reduced. This is ofparticular importance where Internet Protocol (IP) addresses aretransmitted via RACH (and CPCH).

By speeding up RACH procedures, IP connection embodiments can also workmore quickly. An acceleration of the call setup and RACH processestranslates into a decrease in delay for users in, for example, a WorldWide Web browsing application.

Alternatively (or in addition, depending upon the embodiment), theaverage transmission power of the UE is also reduced. This increases theUL capacity and coverage, especially in a WCDMA scenario where areduction of the average transmission power of a UE causes lessinterference to other users of the network.

Although the invention has been described with reference to a number ofspecific embodiments, it will be appreciated by those skilled in the artthat the invention can be embodied in many other forms.

1. A method of initiating a telecommunications uplink from a mobileterminal to a telecommunications network, the mobile terminal having atransmission chain including a baseband stage, a power amplificationstage and an antenna, the method including the steps of: (a)transmitting a preamble signal from the mobile terminal, the preamblesignal being transmitted in accordance with a transmission parameter ofthe mobile terminal; (b) determining whether a base station hassuccessfully received the preamble signal and if so, establishing anuplink to the base station on the basis of the first transmissionparameter; (c) in the event it is not determined that a base station hassuccessfully received the preamble signal, changing the transmissionparameter, and repeating steps (a) and (b); wherein the transmissionparameter controls one or more of the baseband stage, poweramplification stages and the antenna such that changing the transmissionparameter in step (c) results in an alteration of the signal diversityof one or more preambles as received by the base station.
 2. A methodaccording to claim 1, wherein the transmission chain includes at leasttwo antennae, and the transmission parameter determines which of theantennae the preamble is transmitted from.
 3. A method according toclaim 2, wherein the preamble is transmitted from only one of theantennae at a time.
 4. A method according to claim 1, wherein thetransmission parameter includes a frequency band, each preamble beingtransmitted via the frequency band indicated by the current transmissionparameter.
 5. A method according to claim 1, wherein the transmissionchain includes a plurality of antennae in an antenna array, anddirectionality of a beam formed by signals transmitted from the array isselected for each preamble transmission based on the transmissionparameter.
 6. A method according to claim 5, wherein the transmissionchain includes a phase shifting means for shifting the phase of thesignals supplied to the individual antennae in the antenna array, thephase shifters being controllable on the basis of the transmissionparameter.
 7. A method according to claim 1, wherein the uplink isestablished in accordance with the transmission parameter used when thebase station successfully received the preamble.
 8. A method accordingto claim 1, wherein the transmission parameter includes a power level atwhich each preamble is transmitted, the power level being increasedbetween at least some sequentially adjacent preamble transmissions.
 9. Amobile telecommunications terminal configured to initiate atelecommunications uplink to a telecommunications network, the mobileterminal having a transmission chain including a baseband stage, a poweramplification stage and an antenna and being configured to: (a) transmita preamble signal in accordance with a transmission parameter of themobile terminal; (b) determine whether a base station has successfullyreceived the preamble signal and if so, to establish an uplink to thebase station on the basis of the first transmission parameter; (c) inthe event it is not determined that a base station has successfullyreceived the preamble signal, change the transmission parameter, andrepeat (a) and (b); wherein the transmission parameter controls one ormore of the baseband stage, power amplification stages and the antennasuch that changing of the transmission parameter in (c) results in analteration of the signal diversity of one or more subsequent preamblesas received by the base station.
 10. A mobile telecommunicationsterminal according to claim 9, wherein the transmission chain includesat least two antennae, and the transmission parameter determines whichof the antennae the preamble is transmitted from.
 11. A mobiletelecommunications terminal according to claim 10, wherein the preambleis transmitted from only one of the antennae at a time.
 12. A mobiletelecommunications terminal according to claim 9, wherein thetransmission parameter includes a frequency band, each preamble beingtransmitted via the frequency band indicated by the current transmissionparameter.
 13. A mobile telecommunications terminal according to claim9, wherein the transmission chain includes a plurality of antennae in anantenna array, and directionality of a beam formed by signalstransmitted from the array is selected for each preamble transmissionbased on the transmission parameter.
 14. A mobile telecommunicationsterminal according to claim 13, wherein the transmission chain includesa phase shifting means for shifting the phase of the signals supplied tothe individual antennae in the antenna array, the phase shifters beingcontrollable on the basis of the transmission parameter.
 15. A mobiletelecommunications terminal according to claim 9, wherein the uplink isestablished in accordance with the transmission parameter used when thebase station successfully received the preamble.
 16. A mobiletelecommunications terminal according to claim 9, wherein thetransmission parameter includes a power level at which each preamble istransmitted, the power level being increased between at least somesequentially adjacent preamble transmissions.